This invention relates generally to self-tapping dental implants and particularly to techniques for forming roughened surfaces on self-tapping dental implants.
Dental implants are used to provide a tooth-like structure in areas where both the tooth and the root are missing. Areas where all tooth structure is absent, called edentulous regions, may exist where one or more teeth have been lost.
A typical dental implant has a generally cylindrical structure. The cylindrical body of the implant is secured into the jawbone with the upper proximal edge or neck portion located at or above the jawbone crest. The neck portion often has a threaded bore for receiving an abutment that mounts the artificial tooth. The opposite end of the implant, called the distal end, is located in a position anchored within the jawbone.
By a process known as osseointegration, the implant becomes integrally bonded with the bone tissue over time. In this way the implant may be very securely retained in the jaw structure.
Self-tapping implants include at least one longitudinal cutting groove extending along the length of the implant body. Usually the cutting groove extends a substantial portion of the length of the implant down to its distal end. Two or more cutting grooves may be circumferentially spaced about the implant.
As the implant body is rotated into the bone structure, the cutting groove scrapes away bone tissue like a tap. These bone tissue fragments may be secured inside implant body openings adjacent the groove. Further, the bone fragments may re-grow to form bone that is interengaged with the implant.
Self-tapping dental implants have many advantages. One important advantage is that the implantologist is able to save time during the implantation process. Since the implant simultaneously taps the bone during insertion, a separate tapping stage is not necessary. This time saving results in economies as well as decreased air exposure to the exposed implantation site and, therefore, decreased likelihood of infection. In addition, self-tapping implants may have better stability and more intimate contact with the bone. Thus, self-tapping implants may achieve better osseointegration inter alia because of the bone fragments formed in the cutting process and the enhanced opportunity for the growth of new bone tissue.
Self-tapping implants should have relatively sharp cutting edges to avoid the necessity for very high insertion torque during installation. Greater insertion torque during insertion can damage the engaging neck portion at the proximal end of the implant. In addition, the need for high torque may result in an implant that is not fully seated in the bone tissue. Also, the need for high torque may increase the installation time.
Random surface roughness in dental implants, in general, increases the stability and osseointegration of those implants. One theory is that the roughened surface provides spacing between the implant and the bone surface where osseointegration may occur. While it is possible to machine roughened features onto the dental implant surface, random roughness may be more effective in achieving osseointegration.
One explanation for the integration that occurs due to surface roughening is that osteoblast-like cells cover the implant surface to integrate the bone. These cells are apparently able to attach themselves to the implant surface better when that surface is rough. Generally the micromorphologic characteristics of the surface determine the response of these cells to the implant.
Random surface roughness may result from either subtractive or additive processes. An example of a subtractive process is particle bombardment of the surface. Particle bombardment processes include grit blasting with titanium oxide or aluminum oxide. The amount of roughness achieved may be different depending on the particle size, force and duration. Another subtractive process is acid etching the surface, for example, using hydrofluoric acid. Similarly, ion etching, chemical milling, laser etching, and spark erosion may have applicability in dental implant surface roughening.
Additive processes may result in the build up of rough textured surface features on dental implants. Examples of additive processes include the molten titanium plasma spray or "TPS" process and the HA coating process. Generally, bone compatible bioreactive materials such as apatite materials can be used to form an HA coating on the implant surface. Examples of useful apatite materials include hydroxyapatite and whitlocktite.
The HA coatings may be high crystallinity, creating a roughness approximating that achieved with acid etching. Lower density or lower crystallinity HA coatings can match or exceed the roughness achieved through TPS or grit blasting.
The application of random surface roughening techniques to self-tapping implants raises an important issue. While surface roughening, like the self-tapping implant technology, aids in osseointegration, surface roughening, dulls the cutting edge or surface. In turn, this dulled edge increases the friction between the implant and the bone during installation. As a result, the necessary installation torque is increased, giving rise to the possibility of the problems attendant to increased torque, discussed above.
It would be very desirable to have a technique which enables self-tapping implants to be surface roughened without the need for increased insertion torques. Such techniques could enable the advantages of both the self-tapping technology and the random surface roughness technology to be achieved in a single implant.
Some self-tapping implants roughen a middle portion of the body and leave the entire distal end relatively unroughened. These implants maintain a sharp cutting edge. But, the benefits of roughening are not fully achieved on the implant body since a significant portion of the submerged implant is not roughened. An implant that had a roughened distal portion yet maintained a sharp cutting edge would be advantageous.